Add pull request reference to CHANGELOG
Add pull request reference to CHANGELOG

This makes it easier for users to find more details about changes from the CHANGELOG.

See https://github.com/adhearsion/adhearsion/commit/f5d6f2e14aa1eddb4c88141ab598b456fd1f8091#commitcomment-5317062
renemendoza/adhearsion,renemendoza/adhearsion,cloudvox/adhearsion,adhearsion/adhearsion,kares/adhearsion,cloudvox/adhearsion,renemendoza/adhearsion,kares/adhearsion,adhearsion/adhearsion,cloudvox/adhearsion,adhearsion/adhearsion,cloudvox/adhearsion,adhearsion/adhearsion